The vaccines are designed to target the KP.2 strain of the SARS-CoV-2 virus. In June, the Food and Drug Administration (FDA) told manufacturers to make vaccines targeting the JN.1 variant, but later told them to target the KP.2 strain if possible, given the continued evolution of the virus. 

The vaccine is approved for people 12 and older, with emergency use authorization granted for children aged between 6 months and 4 years of age.

“Given waning immunity of the population from previous exposure to the virus and from prior vaccination, we strongly encourage those who are eligible to consider receiving an updated COVID-19 vaccine to provide better protection against currently circulating variants,” Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, said in a statement. 

The highest viral activity right now is in the West, according to wastewater data from the CDC, but a “high” or “very high” level of COVID-19 virus is being detected in wastewater in almost every state. And viral levels are much higher nationwide than they were this time last year and started increasing earlier in the summer. 

Federal wastewater data indicates viral activity has been on the rise since mid-May. 

Moderna said it expects its updated vaccine to be available in the “coming days,” which Pfizer echoed in its own statement, saying it would “begin shipping immediately.” 

The arrival of new vaccines should add an important layer of protection for Americans, especially the ones most at risk for severe infections. While most Americans have some level of immunity from previous vaccinations, infection or both, older and immunocompromised people can’t mount as strong an immune defense and remain most at risk.  

But the availability of vaccines hasn’t translated into people getting them—only about 20 percent of Americans received last year’s updated shot.